When it comes time to adjust tonality in an image, most people immediately apply Curves. Now, Curves is a very powerful tool, and it usually produces good results. However, Curves is not the only method of adjusting tonality. Another excellent method is to use Blend modes.
Figure 1 shows a scene of a sunset on a beach. The foreground looks okay, but the sky is too light and lacks contrast. When the shot was taken, the sky looked more dramatic than shown in this image. This is because some extra exposure was given to make sure that the water did not come out too dark. This lightened up the sky.
This problem can easily be fixed by applying a blend mode. Now, it might seem like the obvious thing to do is duplicate the Beach Sunset layer by dragging the layer down to the Create a new layer icon at the bottom of the Layers panel and apply a Blend mode to the duplicated layer. This would create a second layer as shown in Figure 2.
However, this will cause the file size to increase substantially. This can be seen if the Document Sizes is displayed on the status bar in the lower left corner of the document window (see Figure 3). The size on the left is the approximate size of the file if it were to be flattened to a single layer. For this image, this size is shown as 36.0 Mbs. This is also the size of the original image as the original image was also one layer. The size on the right is the approximate size of the file with all of the layers. For this image, this size is shown as 72.0 Mbs. In other words, duplicating the layer has doubled the image size.
There is a better way to use Blend modes. Starting with the original image, an adjustments layer is added by selecting an adjustment layer from the Adjustments panel (see Figure 4). For this image, a Curves adjustment layer is added (see Figure 5).
At this point, it might appear that that a curve is going to be used to adjust the tonality. However, this is not the case. The Curves adjustment layer was simply added so that a Blend mode could be applied to the new layer. It is the Blend mode -- not the curve -- that will darken the sky. The important point here is that a Blend mode will have the same affect when applied to an adjustment layer as it will have when applied to a layer that is a duplicate of the original image. This is shown in Figures 6 and 7. Figure 6 shows the image when the Beach Sunset layer was duplicated and the Blend mode of the duplicate layer was set to the Multiply Blend mode. Figure 7 shows the image when a Curves adjustment layer was added and the Blend mode of the adjustment layer was set to the Multiply Blend mode.
As can be seen, the Multiply Blend mode had the same affect when applied to the adjustment layer as when applied to a duplicate of the original image.
The advantage to using an adjustment layer, instead of duplicating an image layer, is that the file size does not increase much when an adjustment layer is added. Earlier, when the Beach Sunset layer was duplicated, the file size increased from 36.0 Mbs to 72.0 Mbs. Conversely, when the Curves layer was added, the file size stayed at 36.0 Mbs.
Since using an adjustment layer will keep the file size smaller than duplicating the Beach Sunset layer, a Curves layer will be used for the Blend mode editing for this image. The Layers panel will now appear as shown in Figure 8.
An important point is that, while a Curves adjustment layer was used in this case, any of the adjustment layers could have been used. For instance, a Hue/Saturation, Brightness/Contrast, or Color Balance adjustment layer could have been used instead.
The next step is to change the Blend mode of the Curves layer. This is easily done by selecting a Blend mode from the Blend mode pop-up menu (see Figure 9).
As can be seen, there are many Blend mode options in the pop-up menu (while it is beyond the scope of this article to cover the various blend modes; a detailed explanation of each of the blend modes can be found in the Blend Mode article series on this web site).
The best choice for enhancing the sky in this image is the Multiply Blend mode. In short, the Multiply Blend mode increases image density. Figure 10 shows the image with the Blend mode of the Curves layer set to Multiply. Figure 11 shows the Layers panel.
The problem, at this point, is that the Multiply Blend mode has darkened the entire image rather than just the sky. It is necessary to apply a mask to the Curves layer that isolates the darkening to the sky. Actually, the Curves layer already has a mask, but it is entirely white. So, the current mask isn't actually doing anything to modify this layer's affect. One easy way to modify the mask is to click on the mask and press Control+I on a PC or Command+I on a Mac. This will invert the color in the mask. The mask is now filled with Black (see Figure 12), so the layer is no longer darkening the image.
To add darkening to just the sky, the Brush is chosen from the Tools panel (see Figure 13). Then, the Brush is set to white (see Figure 13), the Brush size and hardness is adjusted (see Figure 14), and the Opacity and Flow are adjusted (see Figure 15).
Figures 19 and 20 show the original and final images.
Of course, just having another technique doesn't do any good unless it has some advantages. The advantage of using the Blend mode technique is that there are a lot of Blend modes to choose from. That means that there are a lot of tonal effects that can be chosen. This can sometimes provide solutions to difficult tonal editing problems.
Figures 21 and 22 demonstrate this point. Figure 21 shows an image before any editing. This image was particularly challenging to edit. This scene was shot from a desert plateau overlooking the desert valley below as a major storm was just breaking up. The sun was setting and had just broken through the clouds to create a dramatically lit scene with the clouds seeming to glow from within from the light. The mountain ridges were in silhouette and contrasted in tone with the dramatically lit clouds. The problem was that the clouds came out lackluster in the image. They seemed somewhat dull and did not dramatically separate from the dark mountain ridges as well as they should have.
Various attempts at Curves, Levels, dodging, and other methods never produced the desired effect. An additional problem with these approaches was that they all required masks to protect the dark mountain ridges from the affects of the editing. These masks required a lot of finessing to produce masks that were not obvious at the places where the white clouds touched the dark mountains.
The Color Dodge Blend mode solved the problem. An adjustment layer was added and set to the Color Dodge Blend mode. This lightened the clouds but left the dark ridges relatively unaffected. Thus, the clouds picked up the feeling of diffused light and separated much better from the mountains. Furthermore, since the Color Dodge Blend mode had little noticeable affect on the dark areas, the desired affect blended seamlessly from the light clouds to the dark mountains with no mask required. Thus, the use of the Color Dodge Blend Mode produced the desired effect without having to do a lot of work to finesse a Curve and create a complicated mask.
Using Blend modes to modify tonality not only provides another option for tonal editing but can sometimes provide solutions that are simpler and more elegant than Curves.